A fingerprint has been most frequently used among various fields of biometrics due to a high identification rate and security, and a substantially enough amount of personal data is currently retained. Recently, with the development of an automatic fingerprint recognition technology, a fingerprint recognition system for acquiring a fingerprint in real time has been required.
As the prices of fingerprint sensors for use in such a fingerprint recognition system have been recently reduced, the fingerprint sensors are applied to not only a special security device but also peripheral devices of personal computers, such as a keyboard, a mouse, and the like, so as to be used for electronic commerce.
Therefore, in order to enter such a market, a technology for manufacturing a fingerprint sensor that is easy to use, consumes low power, and has a compact size, a low price and high definition should be secured. Researches have been conducted over the last several decades to develop a technology for electrically sensing a fingerprint. Fingerprint sensing methods proposed up to the present time may be generally classified into an optical type, a thermal type, and a capacitive type.
According to the capacitive type that is based on the principle in which capacitance varies with a distance between two electrodes, a fingerprint image may be obtained by recognizing a valley and a ridge of a fingerprint on the basis of a difference between capacitance generated between a sensing electrode and the valley of the fingerprint and capacitance generated between the sensing electrode and the ridge of the fingerprint. Since the capacitive type can be implemented using a standard complementary metal oxide semiconductor (CMOS) process technology, the capacitive type enables a simple structure of a sensor and does not require an additional device or a special process, thereby bringing about the advantages of compact size, low power consumption and low cost. However, the sensed capacitance of the ridge or the valley has a very small value such as several femto farads, and electrodes generally formed of indium tin oxide (ITO) in a touch screen panel have parasitic elements such as capacitance and resistance which may cause serious performance degradation in terms of touch sensitivity and accuracy.